As a repulsion type circuit breaker, there is a two-point switch circuit breaker (for example, Patent Document 1) wherein two movable contact points open simultaneously.
FIG. 6 shows a circuit breaker of Patent Document 1. Reference numeral 1 is a case made of molded resin, and reference numeral 2 a cover made of molded resin, wherein a power source side terminal block 3, a second movable contact 4, a first movable contact 5, an arc extinguishing chamber 6, a switching mechanism 7, an overcurrent tripping device 8, a load side terminal block 9, and the like, are housed in the case 1.
The second movable contact 4 is pivotally supported by a support fitting 11 via a shaft 10 in the vicinity of a V-shaped portion of the second movable contact 4, and is urged toward the first movable contact 5 by a return spring 12 placed on the shaft 10.
Then, a lower end portion of the second movable contact 4 is connected to the power source side terminal block 3 via a lead 13. The support fitting 11 is fixed to the case 1 with a screw 14. Also, the power source side terminal block 3 is fixed to the case 1 with a screw 15.
The overcurrent tripping device 8 disposed between the first movable contact 5 and load side terminal block 9 includes a bimetal 16 and an electromagnet (not shown), and the electromagnet has a configuration wherein a coil 19 is coiled around an iron core 18 joined to a yoke 17, and a return spring 21 is provided between an armature 20, opposing the iron core 18 and pivotally supported by the yoke 17, and the yoke 17.
The bimetal 16 is joined to an L-shaped fitting 22, and the L-shaped fitting 22 is fixed with a screw 25 to a flat conductor 24 connected to the first movable contact 5 via a lead 23. The flat conductor 24 is fixed to the case 1 with a screw 26, and the yoke 17 is fixed to the case 1 with a screw 27. An upper end portion of the bimetal 16 and one end of the coil 19 are connected via a lead 28, and the other end of the coil 19 is connected to the load side terminal block 9.
Also, the circuit breaker of FIG. 6 is of a structure wherein the power source side terminal block 3 and support fitting 11 supporting the second movable contact 4 are unitized by being integrally assembled on a common insulating base 33, and the unit is fitted into the case 1 inside which the first movable contact 5 and switching mechanism 7 are fitted, from a bottom surface side thereof, and covered with a base cover 41.
The circuit breaker in the closed condition shown in FIG. 6 is such that current flows from the power source side terminal block 3 through the lead 13, second movable contact 4, first movable contact 5, lead 23, flat conductor 24, L-shaped fitting 22, bimetal 16, lead 28, and coil 19, to the load side terminal block 9. When an energizing current in the circuit breaker reaches an overload condition, the bimetal 16 distorts, releasing a lock of the switching mechanism 7, and the first movable contact 5 is opened. Also, when a large current such as a short circuit current flows through the circuit breaker, the armature 20 attracted to the iron core 18 releases the lock of the switching mechanism 7, but as the currents flowing through the second movable contact 4 and first movable contact 5 flow in mutually opposite directions, as shown by arrows in the drawing, the second movable contact 4 and first movable contact 5 are such that the second movable contact 4 is driven in a counterclockwise direction in the drawing, and the first movable contact 5 in a clockwise direction in the drawing, before the release of the switching mechanism lock, due to an electromagnetic repulsion acting between the second movable contact 4 and first movable contact 5. Because of this, an arc is generated between the two contacts 4 and 5, increasing the arc voltage, after which, the switching mechanism operates under a command from the overcurrent tripping device 8, and a current limiting and breaking is carried out in a short time.